* BHP, Fortescue agree to add Mysteel indices to 2018 contracts-sources
* Marks biggest shake-up of iron ore contracts in years
* Move comes as China seeks greater commodities pricing clout
By Ruby Lian and Josephine Mason
SHANGHAI, Jan 25 (Reuters) - Chinese steelmakers have succeeded in a push to include domestic iron ore price indices in some 2018 annual supply contracts with global miners, four industry sources said, as the world's top buyer boosts its clout over pricing of major commodities.
The move marks a major step in the evolution of iron ore pricing after the industry abandoned decades-old closed door talks between miners and steelmakers in 2010 in favour of a daily price index.
While it's not expected to have a big impact on prices, it will boost the confidence of Chinese buyers that prices reflect domestic demand and is in line with China's desire to increase its influence over commodity pricing.
"China has always aimed to gain pricing influence in resources, including plans to launch crude oil futures," said Zhou Tao, an analyst with Citic Futures in Shanghai.
Steelmakers and miners currently price annual contracts against benchmark indices set by agencies outside China, mainly S&P Global Platts based on its assessment of the market.
BHP Billiton has agreed with two leading Chinese steel mills to include the China-based Mysteel price index alongside the Platts index for contracts for the new fiscal year, two sources with direct knowledge of the matter said.
Fortescue Metals Group, the world's fourth-largest iron ore miner, has also agreed to include price indices published by Mysteel and local rival Custeel in price setting, Custeel and a source at a steel mill said.
China imported a record 1.07 billion tonnes of iron ore in 2017, worth about $80 billion at current prices, accounting for more than 80 percent of the country's total consumption.
Miners have previously adopted indices other than Platts for spot market or electronic platform sales, including the Metal Bulletin Iron Ore Index .IO62-CNO=MB, but annual contracts make up the bulk of sales.
Mysteel, owned by internet platform operator Shanghai Ganglian, declined to comment. Custeel's chief analyst Hu Yanping said Fortescue will use its iron ore price index as part of its payment scheme.
BHP, which used Mysteel for spot cargoes in 2015, said it was committed to the development of a range of credible iron ore indices.
"The use of Mysteel Iron Ore Index supports BHP's wish to meet customer demand and ensure transparent and robust pricing," it said in an emailed statement.
Fortescue did not comment directly on price formulas but said it has been working with customers in China, its largest market, and recognised the increasing maturity of Chinese indices.
The pricing change was spearheaded by the China Iron & Steel Association, an industry body representing medium and large-sized mills, which raised the issue with foreign miners last year, a source familiar with the matter said.
Iron ore prices have rebounded in the past couple of years, but most forecasters see prices weakening in 2018 on the back of slower Chinese economic growth and Beijing's efforts to tackle overcapacity and air pollution.
"Miners have high sales pressure and have offered to use Chinese indices for settlement," said one mill source, declining to be named as he's not authorised to speak to media.
Citic's Zhou said there was little difference between Platts and Mysteel indices on a monthly average basis, but prices could differ on particular days, which had led to some dissatisfaction from Chinese mills.
S&P Global Platts head of Metals Vera Blei said the company's benchmarks aimed to reflect the market, and the company actively consults with market participants.
Recent formal consultations had allowed Platts to evolve its benchmarks, in line with changes in the iron ore market as it became more precise and efficient, she said in an emailed statement.
Brazil's Vale said in an email the company uses different market indices for spot deals, while Rio Tinto said iron ore pricing was confidential.
Reporting by Ruby Lian and Josephine Mason; Additional reporting by Manolo Serapio Jr in MANILA, Sonali Paul in MELBOURNE, Shanghai newsroom, Luciano Costa de Paula in SAO PAULO; editing by Richard Pullin